A fuel injector including a valve-closure member that has an extension at a downstream end has been described in, e.g., German Patent No. 37 10 467. As described, the valve-closure member coacts with a valve-seat surface to form a sealing seat that is constituted by a recess at the downstream end of the nozzle body. The recess is conically shaped until the transition into a cylindrical opening of the nozzle body. In order to generate a high surface pressure at the sealing line, the valve-closure member has a small radius in the region of the sealing seat in the transition to a conical part at the downstream end.
The cylindrical extension is positioned downstream from the conical part on the valve-closure member, the cylindrical extension projecting into the opening in the nozzle body. With the fuel injector in the idle state, the extension just fails to protrude out of the nozzle body at the downstream end of the opening. The extension forms an annular gap with the opening. Multiple spray openings, whose inlet openings lie within the annular gap, are present in a perforated spray disk positioned at the downstream end of the nozzle body.
The fact that the extension projects into the opening of the nozzle body is a disadvantage of the fuel injector described above. The annular gap that is formed exhibits a constant cross section during the entire opening period of the fuel injector. Only the length of the annular gap changes during the valve needle stroke. The annular gap thereby influences the fuel flow during the entire spray discharge period. A specific intervention at the beginning of the spray discharge operation in which there is a reduced or completely nullified effect when the fuel injector is completely open, is thus not possible.
The transitions between the individual sections of the valve-closure member, which are optimized in terms of flow engineering, ensure a fuel flow with little flow loss. The momentum of the fuel emerging from the fuel injector is high. If the emerging fuel stream is not conditioned downstream from the extension, the result is a large penetration depth of the sprayed fuel. Depending on the combustion procedure and combustion chamber geometry, this can have a disadvantageous effect on the combustion process.
It is also disadvantageous that influencing the flow in a swirl-producing valve with a swirl disk positioned upstream from the sealing seat interferes with the formation of a swirled flow. The flow losses result in a degradation of stream conditioning.